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ffmpeg/libavformat/applehttp.c
Panagiotis H.M. Issaris 795d9594cf applehttp: Fix seeking in streams not starting at DTS=0 
The Apple HTTP Live Streaming demuxer's implementation of
seeking searches for the MPEG TS segment which contains the
requested timestamp.  In its current implementation it assumes
that the first segment will start from 0.

But, MPEG TS streams do not necessarily start with timestamp
(near) 0, causing seeking to fail for those streams.

This also occurs when using live streaming of HTTP Live Streams.
In this case sliding playlists may be used, which means that in
that case only the last x encoded segments are stored, the earlier
segments get deleted from disk and removed from the playlist.
Because of this, when starting playback of a stream in the middle
of such a broadcast, the initial segment fetched after parsing
the m3u8 playlist will not start from timestamp (near) 0, causing
(the admittedly limited live) seeking to fail.

This patch changes this demuxers seeking implementation to use
the initial DTS as an offset for searching the segments containing
the requested timestamp.

Signed-off-by: Martin Storsjö <martin@martin.st>
2011-11-18 11:33:44 +02:00

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/*
* Apple HTTP Live Streaming demuxer
* Copyright (c) 2010 Martin Storsjo
*
* This file is part of Libav.
*
* Libav is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* Libav is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* Apple HTTP Live Streaming demuxer
* http://tools.ietf.org/html/draft-pantos-http-live-streaming
*/
#include "libavutil/avstring.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/mathematics.h"
#include "libavutil/opt.h"
#include "libavutil/dict.h"
#include "avformat.h"
#include "internal.h"
#include <unistd.h>
#include "avio_internal.h"
#include "url.h"
#define INITIAL_BUFFER_SIZE 32768
/*
* An apple http stream consists of a playlist with media segment files,
* played sequentially. There may be several playlists with the same
* video content, in different bandwidth variants, that are played in
* parallel (preferrably only one bandwidth variant at a time). In this case,
* the user supplied the url to a main playlist that only lists the variant
* playlists.
*
* If the main playlist doesn't point at any variants, we still create
* one anonymous toplevel variant for this, to maintain the structure.
*/
enum KeyType {
KEY_NONE,
KEY_AES_128,
};
struct segment {
int duration;
char url[MAX_URL_SIZE];
char key[MAX_URL_SIZE];
enum KeyType key_type;
uint8_t iv[16];
};
/*
* Each variant has its own demuxer. If it currently is active,
* it has an open AVIOContext too, and potentially an AVPacket
* containing the next packet from this stream.
*/
struct variant {
int bandwidth;
char url[MAX_URL_SIZE];
AVIOContext pb;
uint8_t* read_buffer;
URLContext *input;
AVFormatContext *parent;
int index;
AVFormatContext *ctx;
AVPacket pkt;
int stream_offset;
int finished;
int target_duration;
int start_seq_no;
int n_segments;
struct segment **segments;
int needed, cur_needed;
int cur_seq_no;
int64_t last_load_time;
char key_url[MAX_URL_SIZE];
uint8_t key[16];
};
typedef struct AppleHTTPContext {
int n_variants;
struct variant **variants;
int cur_seq_no;
int end_of_segment;
int first_packet;
int64_t first_timestamp;
AVIOInterruptCB *interrupt_callback;
} AppleHTTPContext;
static int read_chomp_line(AVIOContext *s, char *buf, int maxlen)
{
int len = ff_get_line(s, buf, maxlen);
while (len > 0 && isspace(buf[len - 1]))
buf[--len] = '\0';
return len;
}
static void free_segment_list(struct variant *var)
{
int i;
for (i = 0; i < var->n_segments; i++)
av_free(var->segments[i]);
av_freep(&var->segments);
var->n_segments = 0;
}
static void free_variant_list(AppleHTTPContext *c)
{
int i;
for (i = 0; i < c->n_variants; i++) {
struct variant *var = c->variants[i];
free_segment_list(var);
av_free_packet(&var->pkt);
av_free(var->pb.buffer);
if (var->input)
ffurl_close(var->input);
if (var->ctx) {
var->ctx->pb = NULL;
av_close_input_file(var->ctx);
}
av_free(var);
}
av_freep(&c->variants);
c->n_variants = 0;
}
/*
* Used to reset a statically allocated AVPacket to a clean slate,
* containing no data.
*/
static void reset_packet(AVPacket *pkt)
{
av_init_packet(pkt);
pkt->data = NULL;
}
static struct variant *new_variant(AppleHTTPContext *c, int bandwidth,
const char *url, const char *base)
{
struct variant *var = av_mallocz(sizeof(struct variant));
if (!var)
return NULL;
reset_packet(&var->pkt);
var->bandwidth = bandwidth;
ff_make_absolute_url(var->url, sizeof(var->url), base, url);
dynarray_add(&c->variants, &c->n_variants, var);
return var;
}
struct variant_info {
char bandwidth[20];
};
static void handle_variant_args(struct variant_info *info, const char *key,
int key_len, char **dest, int *dest_len)
{
if (!strncmp(key, "BANDWIDTH=", key_len)) {
*dest = info->bandwidth;
*dest_len = sizeof(info->bandwidth);
}
}
struct key_info {
char uri[MAX_URL_SIZE];
char method[10];
char iv[35];
};
static void handle_key_args(struct key_info *info, const char *key,
int key_len, char **dest, int *dest_len)
{
if (!strncmp(key, "METHOD=", key_len)) {
*dest = info->method;
*dest_len = sizeof(info->method);
} else if (!strncmp(key, "URI=", key_len)) {
*dest = info->uri;
*dest_len = sizeof(info->uri);
} else if (!strncmp(key, "IV=", key_len)) {
*dest = info->iv;
*dest_len = sizeof(info->iv);
}
}
static int parse_playlist(AppleHTTPContext *c, const char *url,
struct variant *var, AVIOContext *in)
{
int ret = 0, duration = 0, is_segment = 0, is_variant = 0, bandwidth = 0;
enum KeyType key_type = KEY_NONE;
uint8_t iv[16] = "";
int has_iv = 0;
char key[MAX_URL_SIZE];
char line[1024];
const char *ptr;
int close_in = 0;
if (!in) {
close_in = 1;
if ((ret = avio_open2(&in, url, AVIO_FLAG_READ,
c->interrupt_callback, NULL)) < 0)
return ret;
}
read_chomp_line(in, line, sizeof(line));
if (strcmp(line, "#EXTM3U")) {
ret = AVERROR_INVALIDDATA;
goto fail;
}
if (var) {
free_segment_list(var);
var->finished = 0;
}
while (!in->eof_reached) {
read_chomp_line(in, line, sizeof(line));
if (av_strstart(line, "#EXT-X-STREAM-INF:", &ptr)) {
struct variant_info info = {{0}};
is_variant = 1;
ff_parse_key_value(ptr, (ff_parse_key_val_cb) handle_variant_args,
&info);
bandwidth = atoi(info.bandwidth);
} else if (av_strstart(line, "#EXT-X-KEY:", &ptr)) {
struct key_info info = {{0}};
ff_parse_key_value(ptr, (ff_parse_key_val_cb) handle_key_args,
&info);
key_type = KEY_NONE;
has_iv = 0;
if (!strcmp(info.method, "AES-128"))
key_type = KEY_AES_128;
if (!strncmp(info.iv, "0x", 2) || !strncmp(info.iv, "0X", 2)) {
ff_hex_to_data(iv, info.iv + 2);
has_iv = 1;
}
av_strlcpy(key, info.uri, sizeof(key));
} else if (av_strstart(line, "#EXT-X-TARGETDURATION:", &ptr)) {
if (!var) {
var = new_variant(c, 0, url, NULL);
if (!var) {
ret = AVERROR(ENOMEM);
goto fail;
}
}
var->target_duration = atoi(ptr);
} else if (av_strstart(line, "#EXT-X-MEDIA-SEQUENCE:", &ptr)) {
if (!var) {
var = new_variant(c, 0, url, NULL);
if (!var) {
ret = AVERROR(ENOMEM);
goto fail;
}
}
var->start_seq_no = atoi(ptr);
} else if (av_strstart(line, "#EXT-X-ENDLIST", &ptr)) {
if (var)
var->finished = 1;
} else if (av_strstart(line, "#EXTINF:", &ptr)) {
is_segment = 1;
duration = atoi(ptr);
} else if (av_strstart(line, "#", NULL)) {
continue;
} else if (line[0]) {
if (is_variant) {
if (!new_variant(c, bandwidth, line, url)) {
ret = AVERROR(ENOMEM);
goto fail;
}
is_variant = 0;
bandwidth = 0;
}
if (is_segment) {
struct segment *seg;
if (!var) {
var = new_variant(c, 0, url, NULL);
if (!var) {
ret = AVERROR(ENOMEM);
goto fail;
}
}
seg = av_malloc(sizeof(struct segment));
if (!seg) {
ret = AVERROR(ENOMEM);
goto fail;
}
seg->duration = duration;
seg->key_type = key_type;
if (has_iv) {
memcpy(seg->iv, iv, sizeof(iv));
} else {
int seq = var->start_seq_no + var->n_segments;
memset(seg->iv, 0, sizeof(seg->iv));
AV_WB32(seg->iv + 12, seq);
}
ff_make_absolute_url(seg->key, sizeof(seg->key), url, key);
ff_make_absolute_url(seg->url, sizeof(seg->url), url, line);
dynarray_add(&var->segments, &var->n_segments, seg);
is_segment = 0;
}
}
}
if (var)
var->last_load_time = av_gettime();
fail:
if (close_in)
avio_close(in);
return ret;
}
static int open_input(struct variant *var)
{
struct segment *seg = var->segments[var->cur_seq_no - var->start_seq_no];
if (seg->key_type == KEY_NONE) {
return ffurl_open(&var->input, seg->url, AVIO_FLAG_READ,
&var->parent->interrupt_callback, NULL);
} else if (seg->key_type == KEY_AES_128) {
char iv[33], key[33], url[MAX_URL_SIZE];
int ret;
if (strcmp(seg->key, var->key_url)) {
URLContext *uc;
if (ffurl_open(&uc, seg->key, AVIO_FLAG_READ,
&var->parent->interrupt_callback, NULL) == 0) {
if (ffurl_read_complete(uc, var->key, sizeof(var->key))
!= sizeof(var->key)) {
av_log(NULL, AV_LOG_ERROR, "Unable to read key file %s\n",
seg->key);
}
ffurl_close(uc);
} else {
av_log(NULL, AV_LOG_ERROR, "Unable to open key file %s\n",
seg->key);
}
av_strlcpy(var->key_url, seg->key, sizeof(var->key_url));
}
ff_data_to_hex(iv, seg->iv, sizeof(seg->iv), 0);
ff_data_to_hex(key, var->key, sizeof(var->key), 0);
iv[32] = key[32] = '\0';
if (strstr(seg->url, "://"))
snprintf(url, sizeof(url), "crypto+%s", seg->url);
else
snprintf(url, sizeof(url), "crypto:%s", seg->url);
if ((ret = ffurl_alloc(&var->input, url, AVIO_FLAG_READ,
&var->parent->interrupt_callback)) < 0)
return ret;
av_opt_set(var->input->priv_data, "key", key, 0);
av_opt_set(var->input->priv_data, "iv", iv, 0);
if ((ret = ffurl_connect(var->input, NULL)) < 0) {
ffurl_close(var->input);
var->input = NULL;
return ret;
}
return 0;
}
return AVERROR(ENOSYS);
}
static int read_data(void *opaque, uint8_t *buf, int buf_size)
{
struct variant *v = opaque;
AppleHTTPContext *c = v->parent->priv_data;
int ret, i;
restart:
if (!v->input) {
reload:
/* If this is a live stream and target_duration has elapsed since
* the last playlist reload, reload the variant playlists now. */
if (!v->finished &&
av_gettime() - v->last_load_time >= v->target_duration*1000000 &&
(ret = parse_playlist(c, v->url, v, NULL)) < 0)
return ret;
if (v->cur_seq_no < v->start_seq_no) {
av_log(NULL, AV_LOG_WARNING,
"skipping %d segments ahead, expired from playlists\n",
v->start_seq_no - v->cur_seq_no);
v->cur_seq_no = v->start_seq_no;
}
if (v->cur_seq_no >= v->start_seq_no + v->n_segments) {
if (v->finished)
return AVERROR_EOF;
while (av_gettime() - v->last_load_time <
v->target_duration*1000000) {
if (ff_check_interrupt(c->interrupt_callback))
return AVERROR_EXIT;
usleep(100*1000);
}
/* Enough time has elapsed since the last reload */
goto reload;
}
ret = open_input(v);
if (ret < 0)
return ret;
}
ret = ffurl_read(v->input, buf, buf_size);
if (ret > 0)
return ret;
if (ret < 0 && ret != AVERROR_EOF)
return ret;
ffurl_close(v->input);
v->input = NULL;
v->cur_seq_no++;
c->end_of_segment = 1;
c->cur_seq_no = v->cur_seq_no;
if (v->ctx && v->ctx->nb_streams) {
v->needed = 0;
for (i = v->stream_offset; i < v->stream_offset + v->ctx->nb_streams;
i++) {
if (v->parent->streams[i]->discard < AVDISCARD_ALL)
v->needed = 1;
}
}
if (!v->needed) {
av_log(v->parent, AV_LOG_INFO, "No longer receiving variant %d\n",
v->index);
return AVERROR_EOF;
}
goto restart;
}
static int applehttp_read_header(AVFormatContext *s, AVFormatParameters *ap)
{
AppleHTTPContext *c = s->priv_data;
int ret = 0, i, j, stream_offset = 0;
c->interrupt_callback = &s->interrupt_callback;
if ((ret = parse_playlist(c, s->filename, NULL, s->pb)) < 0)
goto fail;
if (c->n_variants == 0) {
av_log(NULL, AV_LOG_WARNING, "Empty playlist\n");
ret = AVERROR_EOF;
goto fail;
}
/* If the playlist only contained variants, parse each individual
* variant playlist. */
if (c->n_variants > 1 || c->variants[0]->n_segments == 0) {
for (i = 0; i < c->n_variants; i++) {
struct variant *v = c->variants[i];
if ((ret = parse_playlist(c, v->url, v, NULL)) < 0)
goto fail;
}
}
if (c->variants[0]->n_segments == 0) {
av_log(NULL, AV_LOG_WARNING, "Empty playlist\n");
ret = AVERROR_EOF;
goto fail;
}
/* If this isn't a live stream, calculate the total duration of the
* stream. */
if (c->variants[0]->finished) {
int64_t duration = 0;
for (i = 0; i < c->variants[0]->n_segments; i++)
duration += c->variants[0]->segments[i]->duration;
s->duration = duration * AV_TIME_BASE;
}
/* Open the demuxer for each variant */
for (i = 0; i < c->n_variants; i++) {
struct variant *v = c->variants[i];
AVInputFormat *in_fmt = NULL;
char bitrate_str[20];
if (v->n_segments == 0)
continue;
if (!(v->ctx = avformat_alloc_context())) {
ret = AVERROR(ENOMEM);
goto fail;
}
v->index = i;
v->needed = 1;
v->parent = s;
/* If this is a live stream with more than 3 segments, start at the
* third last segment. */
v->cur_seq_no = v->start_seq_no;
if (!v->finished && v->n_segments > 3)
v->cur_seq_no = v->start_seq_no + v->n_segments - 3;
v->read_buffer = av_malloc(INITIAL_BUFFER_SIZE);
ffio_init_context(&v->pb, v->read_buffer, INITIAL_BUFFER_SIZE, 0, v,
read_data, NULL, NULL);
v->pb.seekable = 0;
ret = av_probe_input_buffer(&v->pb, &in_fmt, v->segments[0]->url,
NULL, 0, 0);
if (ret < 0)
goto fail;
v->ctx->pb = &v->pb;
ret = avformat_open_input(&v->ctx, v->segments[0]->url, in_fmt, NULL);
if (ret < 0)
goto fail;
v->stream_offset = stream_offset;
snprintf(bitrate_str, sizeof(bitrate_str), "%d", v->bandwidth);
/* Create new AVStreams for each stream in this variant */
for (j = 0; j < v->ctx->nb_streams; j++) {
AVStream *st = avformat_new_stream(s, NULL);
if (!st) {
ret = AVERROR(ENOMEM);
goto fail;
}
st->id = i;
avcodec_copy_context(st->codec, v->ctx->streams[j]->codec);
if (v->bandwidth)
av_dict_set(&st->metadata, "variant_bitrate", bitrate_str,
0);
}
stream_offset += v->ctx->nb_streams;
}
c->first_packet = 1;
c->first_timestamp = AV_NOPTS_VALUE;
return 0;
fail:
free_variant_list(c);
return ret;
}
static int recheck_discard_flags(AVFormatContext *s, int first)
{
AppleHTTPContext *c = s->priv_data;
int i, changed = 0;
/* Check if any new streams are needed */
for (i = 0; i < c->n_variants; i++)
c->variants[i]->cur_needed = 0;;
for (i = 0; i < s->nb_streams; i++) {
AVStream *st = s->streams[i];
struct variant *var = c->variants[s->streams[i]->id];
if (st->discard < AVDISCARD_ALL)
var->cur_needed = 1;
}
for (i = 0; i < c->n_variants; i++) {
struct variant *v = c->variants[i];
if (v->cur_needed && !v->needed) {
v->needed = 1;
changed = 1;
v->cur_seq_no = c->cur_seq_no;
v->pb.eof_reached = 0;
av_log(s, AV_LOG_INFO, "Now receiving variant %d\n", i);
} else if (first && !v->cur_needed && v->needed) {
if (v->input)
ffurl_close(v->input);
v->input = NULL;
v->needed = 0;
changed = 1;
av_log(s, AV_LOG_INFO, "No longer receiving variant %d\n", i);
}
}
return changed;
}
static int applehttp_read_packet(AVFormatContext *s, AVPacket *pkt)
{
AppleHTTPContext *c = s->priv_data;
int ret, i, minvariant = -1;
if (c->first_packet) {
recheck_discard_flags(s, 1);
c->first_packet = 0;
}
start:
c->end_of_segment = 0;
for (i = 0; i < c->n_variants; i++) {
struct variant *var = c->variants[i];
/* Make sure we've got one buffered packet from each open variant
* stream */
if (var->needed && !var->pkt.data) {
ret = av_read_frame(var->ctx, &var->pkt);
if (ret < 0) {
if (!var->pb.eof_reached)
return ret;
reset_packet(&var->pkt);
} else {
if (c->first_timestamp == AV_NOPTS_VALUE)
c->first_timestamp = var->pkt.dts;
}
}
/* Check if this stream has the packet with the lowest dts */
if (var->pkt.data) {
if (minvariant < 0 ||
var->pkt.dts < c->variants[minvariant]->pkt.dts)
minvariant = i;
}
}
if (c->end_of_segment) {
if (recheck_discard_flags(s, 0))
goto start;
}
/* If we got a packet, return it */
if (minvariant >= 0) {
*pkt = c->variants[minvariant]->pkt;
pkt->stream_index += c->variants[minvariant]->stream_offset;
reset_packet(&c->variants[minvariant]->pkt);
return 0;
}
return AVERROR_EOF;
}
static int applehttp_close(AVFormatContext *s)
{
AppleHTTPContext *c = s->priv_data;
free_variant_list(c);
return 0;
}
static int applehttp_read_seek(AVFormatContext *s, int stream_index,
int64_t timestamp, int flags)
{
AppleHTTPContext *c = s->priv_data;
int i, j, ret;
if ((flags & AVSEEK_FLAG_BYTE) || !c->variants[0]->finished)
return AVERROR(ENOSYS);
timestamp = av_rescale_rnd(timestamp, 1, stream_index >= 0 ?
s->streams[stream_index]->time_base.den :
AV_TIME_BASE, flags & AVSEEK_FLAG_BACKWARD ?
AV_ROUND_DOWN : AV_ROUND_UP);
ret = AVERROR(EIO);
for (i = 0; i < c->n_variants; i++) {
/* Reset reading */
struct variant *var = c->variants[i];
int64_t pos = c->first_timestamp == AV_NOPTS_VALUE ? 0 :
av_rescale_rnd(c->first_timestamp, 1,
stream_index >= 0 ? s->streams[stream_index]->time_base.den : AV_TIME_BASE,
flags & AVSEEK_FLAG_BACKWARD ? AV_ROUND_DOWN : AV_ROUND_UP);
if (var->input) {
ffurl_close(var->input);
var->input = NULL;
}
av_free_packet(&var->pkt);
reset_packet(&var->pkt);
var->pb.eof_reached = 0;
/* Locate the segment that contains the target timestamp */
for (j = 0; j < var->n_segments; j++) {
if (timestamp >= pos &&
timestamp < pos + var->segments[j]->duration) {
var->cur_seq_no = var->start_seq_no + j;
ret = 0;
break;
}
pos += var->segments[j]->duration;
}
}
return ret;
}
static int applehttp_probe(AVProbeData *p)
{
/* Require #EXTM3U at the start, and either one of the ones below
* somewhere for a proper match. */
if (strncmp(p->buf, "#EXTM3U", 7))
return 0;
if (strstr(p->buf, "#EXT-X-STREAM-INF:") ||
strstr(p->buf, "#EXT-X-TARGETDURATION:") ||
strstr(p->buf, "#EXT-X-MEDIA-SEQUENCE:"))
return AVPROBE_SCORE_MAX;
return 0;
}
AVInputFormat ff_applehttp_demuxer = {
.name = "applehttp",
.long_name = NULL_IF_CONFIG_SMALL("Apple HTTP Live Streaming format"),
.priv_data_size = sizeof(AppleHTTPContext),
.read_probe = applehttp_probe,
.read_header = applehttp_read_header,
.read_packet = applehttp_read_packet,
.read_close = applehttp_close,
.read_seek = applehttp_read_seek,
};
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