[FFmpeg-devel] avformat/dv: allow returning damaged audio

These potentially damaged packets are marked as corrupt.
The packet length is predicted based on packet length history,
allowing prediction of the common pattern used in NTSC.

Fixes: Ticket8762
Tested-by: Dave Rice <dave@dericed.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavformat/dv.c | 60 ++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 53 insertions(+), 7 deletions(-)

Am Do., 29. Okt. 2020 um 22:59 Uhr schrieb Michael Niedermayer
<michael@niedermayer.cc>:

> +static const AVOption dv_options[] = {
> +    { "dvaudio_concealment", "", OFFSET(dvaudio_concealment), AV_OPT_TYPE_INT  , {.i64 = AUDIO_CONCEAL_DROP}, 0, INT_MAX, DEC, "dvaudio_concealment"},
> +    { "drop",                "", 0                          , AV_OPT_TYPE_CONST, {.i64 = AUDIO_CONCEAL_DROP}, 0, INT_MAX, DEC, "dvaudio_concealment"},
> +    { "pass",                "", 0                          , AV_OPT_TYPE_CONST, {.i64 = AUDIO_CONCEAL_PASS}, 0, INT_MAX, DEC, "dvaudio_concealment"},

Am I correct that the current lavc option "ec" only works for video?

Shouldn't its documentation be extended so it also works for audio
(to avoid adding a new option)?

Carl Eugen

On Thu, 29 Oct 2020, Michael Niedermayer wrote:

> These potentially damaged packets are marked as corrupt.
> The packet length is predicted based on packet length history,
> allowing prediction of the common pattern used in NTSC.
>
> Fixes: Ticket8762

Sync loss is because of invalid timestamps, this is a possible workaround 
for the ticket ignoring the core problem. I will post a patch to fix the 
timestamps, it does not seem hard.

Regards,
Marton


> Tested-by: Dave Rice <dave@dericed.com>
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
> libavformat/dv.c | 60 ++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 53 insertions(+), 7 deletions(-)
>
> diff --git a/libavformat/dv.c b/libavformat/dv.c
> index 3e0d12c0e3..3499cba6f8 100644
> --- a/libavformat/dv.c
> +++ b/libavformat/dv.c
> @@ -34,12 +34,20 @@
> #include "libavcodec/dv_profile.h"
> #include "libavcodec/dv.h"
> #include "libavutil/channel_layout.h"
> +#include "libavutil/opt.h"
> #include "libavutil/intreadwrite.h"
> #include "libavutil/mathematics.h"
> #include "libavutil/timecode.h"
> #include "dv.h"
> #include "libavutil/avassert.h"
> 
> +#define AS_HASH_SIZE 16
> +
> +enum AudioConceal {
> +    AUDIO_CONCEAL_PASS = 1,
> +    AUDIO_CONCEAL_DROP = 0,
> +};
> +
> struct DVDemuxContext {
>     const AVDVProfile*  sys;    /* Current DV profile. E.g.: 525/60, 625/50 */
>     AVFormatContext*  fctx;
> @@ -50,6 +58,9 @@ struct DVDemuxContext {
>     int               ach;
>     int               frames;
>     uint64_t          abytes;
> +    uint8_t           as_pack[AS_HASH_SIZE][5];
> +    uint8_t           as_hash;
> +    int               dvaudio_concealment;
> };
> 
> static inline uint16_t dv_audio_12to16(uint16_t sample)
> @@ -72,7 +83,7 @@ static inline uint16_t dv_audio_12to16(uint16_t sample)
>     return result;
> }
> 
> -static const uint8_t *dv_extract_pack(const uint8_t *frame, enum dv_pack_type t)
> +static const uint8_t *dv_extract_pack(DVDemuxContext *d, const uint8_t *frame, enum dv_pack_type t)
> {
>     int offs;
>     int c;
> @@ -101,6 +112,17 @@ static const uint8_t *dv_extract_pack(const uint8_t *frame, enum dv_pack_type t)
>             break;
>     }
> 
> +    if (t == dv_audio_source || t == dv_audio_control) {
> +        int index = (d->as_hash>>1) & (AS_HASH_SIZE-1);
> +        if (frame[offs] == t) {
> +            memcpy(d->as_pack[index], &frame[offs], sizeof(d->as_pack[index]));
> +        } else if (d->as_pack[index][0] && d->dvaudio_concealment == AUDIO_CONCEAL_PASS) {
> +            return d->as_pack[index];
> +        } else if (d->as_pack[0][0] && d->dvaudio_concealment == AUDIO_CONCEAL_PASS) {
> +            return d->as_pack[0];
> +        }
> +    }
> +
>     return frame[offs] == t ? &frame[offs] : NULL;
> }
> 
> @@ -116,7 +138,7 @@ static const int dv_audio_frequency[3] = {
>  * 3. Audio is always returned as 16-bit linear samples: 12-bit nonlinear samples
>  *    are converted into 16-bit linear ones.
>  */
> -static int dv_extract_audio(const uint8_t *frame, uint8_t **ppcm,
> +static int dv_extract_audio(DVDemuxContext *c, const uint8_t *frame, uint8_t **ppcm,
>                             const AVDVProfile *sys)
> {
>     int size, chan, i, j, d, of, smpls, freq, quant, half_ch;
> @@ -124,7 +146,7 @@ static int dv_extract_audio(const uint8_t *frame, uint8_t **ppcm,
>     const uint8_t *as_pack;
>     uint8_t *pcm, ipcm;
> 
> -    as_pack = dv_extract_pack(frame, dv_audio_source);
> +    as_pack = dv_extract_pack(c, frame, dv_audio_source);
>     if (!as_pack)    /* No audio ? */
>         return 0;
> 
> @@ -137,6 +159,7 @@ static int dv_extract_audio(const uint8_t *frame, uint8_t **ppcm,
>
>     if (freq >= FF_ARRAY_ELEMS(dv_audio_frequency))
>         return AVERROR_INVALIDDATA;
> +    c->as_hash = 2*c->as_hash + smpls;
>
>     size    = (sys->audio_min_samples[freq] + smpls) * 4; /* 2ch, 2bytes */
>     half_ch = sys->difseg_size / 2;
> @@ -153,6 +176,9 @@ static int dv_extract_audio(const uint8_t *frame, uint8_t **ppcm,
>     /* for each DIF channel */
>     for (chan = 0; chan < sys->n_difchan; chan++) {
>         av_assert0(ipcm<4);
> +        c->audio_pkt[ipcm].flags &= ~AV_PKT_FLAG_CORRUPT;
> +        if (as_pack >= c->as_pack[0] && as_pack < c->as_pack[AS_HASH_SIZE])
> +            c->audio_pkt[ipcm].flags |= AV_PKT_FLAG_CORRUPT;
>         pcm = ppcm[ipcm++];
>         if (!pcm)
>             break;
> @@ -224,7 +250,7 @@ static int dv_extract_audio_info(DVDemuxContext *c, const uint8_t *frame)
>     const uint8_t *as_pack;
>     int freq, stype, smpls, quant, i, ach;
> 
> -    as_pack = dv_extract_pack(frame, dv_audio_source);
> +    as_pack = dv_extract_pack(c, frame, dv_audio_source);
>     if (!as_pack || !c->sys) {    /* No audio ? */
>         c->ach = 0;
>         return 0;
> @@ -292,7 +318,7 @@ static int dv_extract_video_info(DVDemuxContext *c, const uint8_t *frame)
>     c->vst->avg_frame_rate = av_inv_q(c->vst->time_base);
>
>     /* finding out SAR is a little bit messy */
> -    vsc_pack = dv_extract_pack(frame, dv_video_control);
> +    vsc_pack = dv_extract_pack(c, frame, dv_video_control);
>     apt      = frame[4] & 0x07;
>     is16_9   = (vsc_pack && ((vsc_pack[2] & 0x07) == 0x02 ||
>                              (!apt && (vsc_pack[2] & 0x07) == 0x07)));
> @@ -312,7 +338,7 @@ static int dv_extract_timecode(DVDemuxContext* c, const uint8_t* frame, char *tc
>     // is only relevant for NTSC systems.
>     int prevent_df = c->sys->ltc_divisor == 25 || c->sys->ltc_divisor == 50;
> 
> -    tc_pack = dv_extract_pack(frame, dv_timecode);
> +    tc_pack = dv_extract_pack(c, frame, dv_timecode);
>     if (!tc_pack)
>         return 0;
>     av_timecode_make_smpte_tc_string2(tc, av_inv_q(c->sys->time_base), AV_RB32(tc_pack + 1), prevent_df, 1);
> @@ -392,7 +418,7 @@ int avpriv_dv_produce_packet(DVDemuxContext *c, AVPacket *pkt,
>         ppcm[i] = c->audio_buf[i];
>     }
>     if (c->ach)
> -        dv_extract_audio(buf, ppcm, c->sys);
> +        dv_extract_audio(c, buf, ppcm, c->sys);
>
>     /* We work with 720p frames split in half, thus even frames have
>      * channels 0,1 and odd 2,3. */
> @@ -460,8 +486,10 @@ void ff_dv_offset_reset(DVDemuxContext *c, int64_t frame_offset)
>  ************************************************************/
> 
> typedef struct RawDVContext {
> +    const AVClass  *class;
>     DVDemuxContext  dv_demux;
>     uint8_t         buf[DV_MAX_FRAME_SIZE];
> +    int             dvaudio_concealment;
> } RawDVContext;
> 
> static int dv_read_timecode(AVFormatContext *s) {
> @@ -502,6 +530,7 @@ static int dv_read_header(AVFormatContext *s)
>
>     if ((ret = dv_init_demux(s, &c->dv_demux)) < 0)
>         return ret;
> +    c->dv_demux.dvaudio_concealment = c->dvaudio_concealment;
>
>     state = avio_rb32(s->pb);
>     while ((state & 0xffffff7f) != 0x1f07003f) {
> @@ -626,6 +655,22 @@ static int dv_probe(const AVProbeData *p)
>     return 0;
> }
> 
> +#define OFFSET(x) offsetof(RawDVContext, x)
> +#define DEC AV_OPT_FLAG_DECODING_PARAM
> +static const AVOption dv_options[] = {
> +    { "dvaudio_concealment", "", OFFSET(dvaudio_concealment), AV_OPT_TYPE_INT  , {.i64 = AUDIO_CONCEAL_DROP}, 0, INT_MAX, DEC, "dvaudio_concealment"},
> +    { "drop",                "", 0                          , AV_OPT_TYPE_CONST, {.i64 = AUDIO_CONCEAL_DROP}, 0, INT_MAX, DEC, "dvaudio_concealment"},
> +    { "pass",                "", 0                          , AV_OPT_TYPE_CONST, {.i64 = AUDIO_CONCEAL_PASS}, 0, INT_MAX, DEC, "dvaudio_concealment"},
> +    { NULL },
> +};
> +
> +static const AVClass dv_demuxer_class = {
> +    .class_name = "DV demuxer",
> +    .item_name  = av_default_item_name,
> +    .option     = dv_options,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
> AVInputFormat ff_dv_demuxer = {
>     .name           = "dv",
>     .long_name      = NULL_IF_CONFIG_SMALL("DV (Digital Video)"),
> @@ -635,4 +680,5 @@ AVInputFormat ff_dv_demuxer = {
>     .read_packet    = dv_read_packet,
>     .read_seek      = dv_read_seek,
>     .extensions     = "dv,dif",
> +    .priv_class     = &dv_demuxer_class,
> };
> -- 
> 2.17.1
>
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On Sat, 31 Oct 2020, Carl Eugen Hoyos wrote:

> Am Do., 29. Okt. 2020 um 22:59 Uhr schrieb Michael Niedermayer
> <michael@niedermayer.cc>:
>
>> +static const AVOption dv_options[] = {
>> +    { "dvaudio_concealment", "", OFFSET(dvaudio_concealment), AV_OPT_TYPE_INT  , {.i64 = AUDIO_CONCEAL_DROP}, 0, INT_MAX, DEC, "dvaudio_concealment"},
>> +    { "drop",                "", 0                          , AV_OPT_TYPE_CONST, {.i64 = AUDIO_CONCEAL_DROP}, 0, INT_MAX, DEC, "dvaudio_concealment"},
>> +    { "pass",                "", 0                          , AV_OPT_TYPE_CONST, {.i64 = AUDIO_CONCEAL_PASS}, 0, INT_MAX, DEC, "dvaudio_concealment"},
>
> Am I correct that the current lavc option "ec" only works for video?
>
> Shouldn't its documentation be extended so it also works for audio
> (to avoid adding a new option)?

This is demuxer not decoder, so ec cannot be used.

Regards,
Marton