Re: [FFmpeg-devel] [PATCH] avformat/mpegtsenc: add pcr_at_keyframe flag

[Marton Balint <cus@passwd.hu>]

On Wed, 28 Sep 2022, Zhao Zhili wrote:

> From: Zhao Zhili <zhilizhao@tencent.com>
>
> Add PCR at keyframe can be undesirable when -pcr_period is
> specified. Add an flag to disable this behavior.

Actually you are disabling the writing of random access indicators, not 
only PCRs. PCR's are just there because it is mandatory when RAI is set 
for PCR pids. In the help text you can mention that it affects writing of 
PCR as well, but in principle you disable RAI, so the option name should 
reflect that instead. Also I kind of prefer not to change the default of 
mpegts_flags from zero, use a negative option instead, like "omit_rai".

Thanks,
Marton


>
> Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
> ---
> doc/muxers.texi         | 2 ++
> libavformat/mpegtsenc.c | 8 ++++++--
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index b2f4326aae..0f576d8096 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -1915,6 +1915,8 @@ Conform to System B (DVB) instead of System A (ATSC).
> Mark the initial packet of each stream as discontinuity.
> @item nit
> Emit NIT table.
> +@item pcr_at_keyframe
> +Write PCR at key frame.
> @end table
>
> @item mpegts_copyts @var{boolean}
> diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
> index 5148a6aecd..808d2c04a2 100644
> --- a/libavformat/mpegtsenc.c
> +++ b/libavformat/mpegtsenc.c
> @@ -112,6 +112,7 @@ typedef struct MpegTSWrite {
> #define MPEGTS_FLAG_SYSTEM_B        0x08
> #define MPEGTS_FLAG_DISCONT         0x10
> #define MPEGTS_FLAG_NIT             0x20
> +#define MPEGTS_FLAG_PCR_AT_KEYFRAME 0x40
>     int flags;
>     int copyts;
>     int tables_version;
> @@ -1566,7 +1567,8 @@ static void mpegts_write_pes(AVFormatContext *s, AVStream *st,
>             q = get_ts_payload_start(buf);
>             ts_st->discontinuity = 0;
>         }
> -        if (key && is_start && pts != AV_NOPTS_VALUE &&
> +        if ((ts->flags & MPEGTS_FLAG_PCR_AT_KEYFRAME) &&
> +            key && is_start && pts != AV_NOPTS_VALUE &&
>             !is_dvb_teletext /* adaptation+payload forbidden for teletext (ETSI EN 300 472 V1.3.1 4.1) */) {
>             // set Random Access for key frames
>             if (ts_st->pcr_period)
> @@ -2269,7 +2271,7 @@ static const AVOption options[] = {
>     { "muxrate", NULL, OFFSET(mux_rate), AV_OPT_TYPE_INT, { .i64 = 1 }, 0, INT_MAX, ENC },
>     { "pes_payload_size", "Minimum PES packet payload in bytes",
>       OFFSET(pes_payload_size), AV_OPT_TYPE_INT, { .i64 = DEFAULT_PES_PAYLOAD_SIZE }, 0, INT_MAX, ENC },
> -    { "mpegts_flags", "MPEG-TS muxing flags", OFFSET(flags), AV_OPT_TYPE_FLAGS, { .i64 = 0 }, 0, INT_MAX, ENC, "mpegts_flags" },
> +    { "mpegts_flags", "MPEG-TS muxing flags", OFFSET(flags), AV_OPT_TYPE_FLAGS, { .i64 = MPEGTS_FLAG_PCR_AT_KEYFRAME }, 0, INT_MAX, ENC, "mpegts_flags" },
>     { "resend_headers", "Reemit PAT/PMT before writing the next packet",
>       0, AV_OPT_TYPE_CONST, { .i64 = MPEGTS_FLAG_REEMIT_PAT_PMT }, 0, INT_MAX, ENC, "mpegts_flags" },
>     { "latm", "Use LATM packetization for AAC",
> @@ -2282,6 +2284,8 @@ static const AVOption options[] = {
>       0, AV_OPT_TYPE_CONST, { .i64 = MPEGTS_FLAG_DISCONT }, 0, INT_MAX, ENC, "mpegts_flags" },
>     { "nit", "Enable NIT transmission",
>       0, AV_OPT_TYPE_CONST, { .i64 = MPEGTS_FLAG_NIT}, 0, INT_MAX, ENC, "mpegts_flags" },
> +    { "pcr_at_keyframe", "Write PCR at key frame",
> +      0, AV_OPT_TYPE_CONST, { .i64 = MPEGTS_FLAG_PCR_AT_KEYFRAME }, 0, INT_MAX, ENC, "mpegts_flags" },
>     { "mpegts_copyts", "don't offset dts/pts", OFFSET(copyts), AV_OPT_TYPE_BOOL, { .i64 = -1 }, -1, 1, ENC },
>     { "tables_version", "set PAT, PMT, SDT and NIT version", OFFSET(tables_version), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 31, ENC },
>     { "omit_video_pes_length", "Omit the PES packet length for video packets",
> -- 
> 2.25.1
>
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