diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
index d1b6b422a2..5f6d738202 100644
--- a/libavformat/rtsp.c
+++ b/libavformat/rtsp.c
@@ -1863,6 +1863,7 @@ int ff_rtsp_fetch_packet(AVFormatContext *s, AVPacket *pkt)
             rt->cur_transport_priv = NULL;
     }
 
+redo:
     if (rt->transport == RTSP_TRANSPORT_RTP) {
         int i;
         int64_t first_queue_time = 0;
@@ -1878,12 +1879,15 @@ int ff_rtsp_fetch_packet(AVFormatContext *s, AVPacket *pkt)
                 first_queue_st   = rt->rtsp_streams[i];
             }
         }
-        if (first_queue_time)
+        if (first_queue_time) {
             wait_end = first_queue_time + s->max_delay;
+        } else {
+            wait_end = 0;
+            first_queue_st = NULL;
+        }
     }
 
     /* read next RTP packet */
- redo:
     if (!rt->recvbuf) {
         rt->recvbuf = av_malloc(RECVBUF_SIZE);
         if (!rt->recvbuf)
diff --git a/libavresample/audio_convert.c b/libavresample/audio_convert.c
index b57d2fa650..371617cc25 100644
--- a/libavresample/audio_convert.c
+++ b/libavresample/audio_convert.c
@@ -378,32 +378,35 @@ int ff_audio_convert(AudioConvert *ac, AudioData *out, AudioData *in)
             }
         }
     } else {
-    switch (ac->func_type) {
-    case CONV_FUNC_TYPE_FLAT: {
-        if (!in->is_planar)
-            len *= in->channels;
-        if (use_generic) {
-            for (p = 0; p < ac->planes; p++)
-                ac->conv_flat_generic(out->data[p], in->data[p], len);
-        } else {
-            for (p = 0; p < ac->planes; p++)
-                ac->conv_flat(out->data[p], in->data[p], len);
+        switch (ac->func_type) {
+        case CONV_FUNC_TYPE_FLAT: {
+            if (!in->is_planar)
+                len *= in->channels;
+            if (use_generic) {
+                for (p = 0; p < ac->planes; p++)
+                    ac->conv_flat_generic(out->data[p], in->data[p], len);
+            } else {
+                for (p = 0; p < ac->planes; p++)
+                    ac->conv_flat(out->data[p], in->data[p], len);
+            }
+            break;
+        }
+        case CONV_FUNC_TYPE_INTERLEAVE:
+            if (use_generic)
+                ac->conv_interleave_generic(out->data[0], in->data, len,
+                                            ac->channels);
+            else
+                ac->conv_interleave(out->data[0], in->data, len, ac->channels);
+            break;
+        case CONV_FUNC_TYPE_DEINTERLEAVE:
+            if (use_generic)
+                ac->conv_deinterleave_generic(out->data, in->data[0], len,
+                                              ac->channels);
+            else
+                ac->conv_deinterleave(out->data, in->data[0], len,
+                                      ac->channels);
+            break;
         }
-        break;
-    }
-    case CONV_FUNC_TYPE_INTERLEAVE:
-        if (use_generic)
-            ac->conv_interleave_generic(out->data[0], in->data, len, ac->channels);
-        else
-            ac->conv_interleave(out->data[0], in->data, len, ac->channels);
-        break;
-    case CONV_FUNC_TYPE_DEINTERLEAVE:
-        if (use_generic)
-            ac->conv_deinterleave_generic(out->data, in->data[0], len, ac->channels);
-        else
-            ac->conv_deinterleave(out->data, in->data[0], len, ac->channels);
-        break;
-    }
     }
 
     out->nb_samples = in->nb_samples;
diff --git a/libavresample/audio_mix.c b/libavresample/audio_mix.c
index 2b3d9f1f7a..12f5d24ba0 100644
--- a/libavresample/audio_mix.c
+++ b/libavresample/audio_mix.c
@@ -47,6 +47,11 @@ struct AudioMix {
     mix_func *mix;
     mix_func *mix_generic;
 
+    int in_matrix_channels;
+    int out_matrix_channels;
+    int output_zero[AVRESAMPLE_MAX_CHANNELS];
+    int input_skip[AVRESAMPLE_MAX_CHANNELS];
+    int output_skip[AVRESAMPLE_MAX_CHANNELS];
     int16_t *matrix_q8[AVRESAMPLE_MAX_CHANNELS];
     int32_t *matrix_q15[AVRESAMPLE_MAX_CHANNELS];
     float   *matrix_flt[AVRESAMPLE_MAX_CHANNELS];
@@ -59,8 +64,8 @@ void ff_audio_mix_set_func(AudioMix *am, enum AVSampleFormat fmt,
                            const char *descr, void *mix_func)
 {
     if (fmt == am->fmt && coeff_type == am->coeff_type &&
-        ( in_channels ==  am->in_channels ||  in_channels == 0) &&
-        (out_channels == am->out_channels || out_channels == 0)) {
+        ( in_channels ==  am->in_matrix_channels ||  in_channels == 0) &&
+        (out_channels == am->out_matrix_channels || out_channels == 0)) {
         char chan_str[16];
         am->mix           = mix_func;
         am->func_descr    = descr;
@@ -82,11 +87,12 @@ void ff_audio_mix_set_func(AudioMix *am, enum AVSampleFormat fmt,
         } else if (out_channels) {
                 snprintf(chan_str, sizeof(chan_str), "[any to %d] ",
                          out_channels);
+        } else {
+            snprintf(chan_str, sizeof(chan_str), "[any to any] ");
         }
         av_log(am->avr, AV_LOG_DEBUG, "audio_mix: found function: [fmt=%s] "
                "[c=%s] %s(%s)\n", av_get_sample_fmt_name(fmt),
-               coeff_type_names[coeff_type],
-               (in_channels || out_channels) ? chan_str : "", descr);
+               coeff_type_names[coeff_type], chan_str, descr);
     }
 }
 
@@ -278,6 +284,12 @@ static void mix_2_to_6_fltp_flt_c(float **samples, float **matrix, int len,
 
 static int mix_function_init(AudioMix *am)
 {
+    /* no need to set a mix function when we're skipping mixing */
+    if (!am->in_matrix_channels || !am->out_matrix_channels) {
+        am->func_descr = "n/a";
+        return 0;
+    }
+
     /* any-to-any C versions */
 
     ff_audio_mix_set_func(am, AV_SAMPLE_FMT_FLTP, AV_MIX_COEFF_TYPE_FLT,
@@ -379,25 +391,34 @@ AudioMix *ff_audio_mix_alloc(AVAudioResampleContext *avr)
             goto error;
         }
 
+        ret = ff_audio_mix_set_matrix(am, matrix_dbl, avr->in_channels);
+        if (ret < 0) {
+            av_log(avr, AV_LOG_ERROR, "error setting mix matrix\n");
+            av_free(matrix_dbl);
+            goto error;
+        }
+
         av_get_channel_layout_string(in_layout_name, sizeof(in_layout_name),
                                      avr->in_channels, avr->in_channel_layout);
         av_get_channel_layout_string(out_layout_name, sizeof(out_layout_name),
                                      avr->out_channels, avr->out_channel_layout);
         av_log(avr, AV_LOG_DEBUG, "audio_mix: %s to %s\n",
                in_layout_name, out_layout_name);
+        av_log(avr, AV_LOG_DEBUG, "matrix size: %d x %d\n",
+               am->in_matrix_channels, am->out_matrix_channels);
         for (i = 0; i < avr->out_channels; i++) {
             for (j = 0; j < avr->in_channels; j++) {
-                av_log(avr, AV_LOG_DEBUG, "  %0.3f ",
-                       matrix_dbl[i * avr->in_channels + j]);
+                if (am->output_zero[i])
+                    av_log(avr, AV_LOG_DEBUG, "  (ZERO)");
+                else if (am->input_skip[j] || am->output_skip[i])
+                    av_log(avr, AV_LOG_DEBUG, "  (SKIP)");
+                else
+                    av_log(avr, AV_LOG_DEBUG, "  %0.3f ",
+                           matrix_dbl[i * avr->in_channels + j]);
             }
             av_log(avr, AV_LOG_DEBUG, "\n");
         }
 
-        ret = ff_audio_mix_set_matrix(am, matrix_dbl, avr->in_channels);
-        if (ret < 0) {
-            av_free(matrix_dbl);
-            goto error;
-        }
         av_free(matrix_dbl);
     }
 
@@ -435,6 +456,7 @@ int ff_audio_mix(AudioMix *am, AudioData *src)
 {
     int use_generic = 1;
     int len = src->nb_samples;
+    int i, j;
 
     /* determine whether to use the optimized function based on pointer and
        samples alignment in both the input and output */
@@ -450,11 +472,35 @@ int ff_audio_mix(AudioMix *am, AudioData *src)
             src->nb_samples, am->in_channels, am->out_channels,
             use_generic ? am->func_descr_generic : am->func_descr);
 
-    if (use_generic)
-        am->mix_generic(src->data, am->matrix, len, am->out_channels,
-                        am->in_channels);
-    else
-        am->mix(src->data, am->matrix, len, am->out_channels, am->in_channels);
+    if (am->in_matrix_channels && am->out_matrix_channels) {
+        uint8_t **data;
+        uint8_t *data0[AVRESAMPLE_MAX_CHANNELS];
+
+        if (am->out_matrix_channels < am->out_channels ||
+             am->in_matrix_channels <  am->in_channels) {
+            for (i = 0, j = 0; i < FFMAX(am->in_channels, am->out_channels); i++) {
+                if (am->input_skip[i] || am->output_skip[i] || am->output_zero[i])
+                    continue;
+                data0[j++] = src->data[i];
+            }
+            data = data0;
+        } else {
+            data = src->data;
+        }
+
+        if (use_generic)
+            am->mix_generic(data, am->matrix, len, am->out_matrix_channels,
+                            am->in_matrix_channels);
+        else
+            am->mix(data, am->matrix, len, am->out_matrix_channels,
+                    am->in_matrix_channels);
+    }
+
+    if (am->out_matrix_channels < am->out_channels) {
+        for (i = 0; i < am->out_channels; i++)
+            if (am->output_zero[i])
+                av_samples_set_silence(&src->data[i], 0, len, 1, am->fmt);
+    }
 
     ff_audio_data_set_channels(src, am->out_channels);
 
@@ -463,7 +509,7 @@ int ff_audio_mix(AudioMix *am, AudioData *src)
 
 int ff_audio_mix_get_matrix(AudioMix *am, double *matrix, int stride)
 {
-    int i, o;
+    int i, o, i0, o0;
 
     if ( am->in_channels <= 0 ||  am->in_channels > AVRESAMPLE_MAX_CHANNELS ||
         am->out_channels <= 0 || am->out_channels > AVRESAMPLE_MAX_CHANNELS) {
@@ -476,9 +522,19 @@ int ff_audio_mix_get_matrix(AudioMix *am, double *matrix, int stride)
         av_log(am->avr, AV_LOG_ERROR, "matrix is not set\n");               \
         return AVERROR(EINVAL);                                             \
     }                                                                       \
-    for (o = 0; o < am->out_channels; o++)                                  \
-        for (i = 0; i < am->in_channels; i++)                               \
-            matrix[o * stride + i] = am->matrix_ ## suffix[o][i] * (scale);
+    for (o = 0, o0 = 0; o < am->out_channels; o++) {                        \
+        for (i = 0, i0 = 0; i < am->in_channels; i++) {                     \
+            if (am->input_skip[i] || am->output_zero[o])                    \
+                matrix[o * stride + i] = 0.0;                               \
+            else                                                            \
+                matrix[o * stride + i] = am->matrix_ ## suffix[o0][i0] *    \
+                                         (scale);                           \
+            if (!am->input_skip[i])                                         \
+                i0++;                                                       \
+        }                                                                   \
+        if (!am->output_zero[o])                                            \
+            o0++;                                                           \
+    }
 
     switch (am->coeff_type) {
     case AV_MIX_COEFF_TYPE_Q8:
@@ -500,7 +556,7 @@ int ff_audio_mix_get_matrix(AudioMix *am, double *matrix, int stride)
 
 int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)
 {
-    int i, o;
+    int i, o, i0, o0;
 
     if ( am->in_channels <= 0 ||  am->in_channels > AVRESAMPLE_MAX_CHANNELS ||
         am->out_channels <= 0 || am->out_channels > AVRESAMPLE_MAX_CHANNELS) {
@@ -513,19 +569,123 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)
         am->matrix = NULL;
     }
 
+    memset(am->output_zero, 0, sizeof(am->output_zero));
+    memset(am->input_skip,  0, sizeof(am->input_skip));
+    memset(am->output_skip, 0, sizeof(am->output_zero));
+    am->in_matrix_channels  = am->in_channels;
+    am->out_matrix_channels = am->out_channels;
+
+    /* exclude output channels if they can be zeroed instead of mixed */
+    for (o = 0; o < am->out_channels; o++) {
+        int zero = 1;
+
+        /* check if the output is always silent */
+        for (i = 0; i < am->in_channels; i++) {
+            if (matrix[o * stride + i] != 0.0) {
+                zero = 0;
+                break;
+            }
+        }
+        /* check if the corresponding input channel makes a contribution to
+           any output channel */
+        if (o < am->in_channels) {
+            for (i = 0; i < am->out_channels; i++) {
+                if (matrix[i * stride + o] != 0.0) {
+                    zero = 0;
+                    break;
+                }
+            }
+        }
+        if (zero) {
+            am->output_zero[o] = 1;
+            am->out_matrix_channels--;
+        }
+    }
+    if (am->out_matrix_channels == 0) {
+        am->in_matrix_channels = 0;
+        return 0;
+    }
+
+    /* skip input channels that contribute fully only to the corresponding
+       output channel */
+    for (i = 0; i < FFMIN(am->in_channels, am->out_channels); i++) {
+        int skip = 1;
+
+        for (o = 0; o < am->out_channels; o++) {
+            if ((o != i && matrix[o * stride + i] != 0.0) ||
+                (o == i && matrix[o * stride + i] != 1.0)) {
+                skip = 0;
+                break;
+            }
+        }
+        if (skip) {
+            am->input_skip[i] = 1;
+            am->in_matrix_channels--;
+        }
+    }
+    /* skip input channels that do not contribute to any output channel */
+    for (; i < am->in_channels; i++) {
+        int contrib = 0;
+
+        for (o = 0; o < am->out_channels; o++) {
+            if (matrix[o * stride + i] != 0.0) {
+                contrib = 1;
+                break;
+            }
+        }
+        if (!contrib) {
+            am->input_skip[i] = 1;
+            am->in_matrix_channels--;
+        }
+    }
+    if (am->in_matrix_channels == 0) {
+        am->out_matrix_channels = 0;
+        return 0;
+    }
+
+    /* skip output channels that only get full contribution from the
+       corresponding input channel */
+    for (o = 0; o < FFMIN(am->in_channels, am->out_channels); o++) {
+        int skip = 1;
+
+        for (i = 0; i < am->in_channels; i++) {
+            if ((o != i && matrix[o * stride + i] != 0.0) ||
+                (o == i && matrix[o * stride + i] != 1.0)) {
+                skip = 0;
+                break;
+            }
+        }
+        if (skip) {
+            am->output_skip[o] = 1;
+            am->out_matrix_channels--;
+        }
+    }
+    if (am->out_matrix_channels == 0) {
+        am->in_matrix_channels = 0;
+        return 0;
+    }
+
 #define CONVERT_MATRIX(type, expr)                                          \
-    am->matrix_## type[0] = av_mallocz(am->out_channels * am->in_channels * \
+    am->matrix_## type[0] = av_mallocz(am->out_matrix_channels *            \
+                                       am->in_matrix_channels  *            \
                                        sizeof(*am->matrix_## type[0]));     \
     if (!am->matrix_## type[0])                                             \
         return AVERROR(ENOMEM);                                             \
-    for (o = 0; o < am->out_channels; o++) {                                \
-        if (o > 0)                                                          \
-            am->matrix_## type[o] = am->matrix_## type[o - 1] +             \
-                                    am->in_channels;                        \
-        for (i = 0; i < am->in_channels; i++) {                             \
-            double v = matrix[o * stride + i];                              \
-            am->matrix_## type[o][i] = expr;                                \
+    for (o = 0, o0 = 0; o < am->out_channels; o++) {                        \
+        if (am->output_zero[o] || am->output_skip[o])                       \
+            continue;                                                       \
+        if (o0 > 0)                                                         \
+            am->matrix_## type[o0] = am->matrix_## type[o0 - 1] +           \
+                                     am->in_matrix_channels;                \
+        for (i = 0, i0 = 0; i < am->in_channels; i++) {                     \
+            double v;                                                       \
+            if (am->input_skip[i])                                          \
+                continue;                                                   \
+            v = matrix[o * stride + i];                                     \
+            am->matrix_## type[o0][i0] = expr;                              \
+            i0++;                                                           \
         }                                                                   \
+        o0++;                                                               \
     }                                                                       \
     am->matrix = (void **)am->matrix_## type;
 
@@ -544,8 +704,5 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)
         return AVERROR(EINVAL);
     }
 
-    /* TODO: detect situations where we can just swap around pointers
-             instead of doing matrix multiplications with 0.0 and 1.0 */
-
     return 0;
 }