[FFmpeg-devel] [PATCH] ALS decoder

[Thilo Borgmann]

>> +        // reconstruct shifted signal
>> +        if (*shift_lsbs)
>> +            for (smp = -1; smp >= -sconf->max_order; smp--)
>> +                raw_samples[smp] >>= *shift_lsbs;
> 
> has that been tested? or is shift_lsbs == 0 for all files we have?
Yes, intensively tested.



>> +/** Computes the bytes left to decode for the current frame
>> + */
>> +static inline unsigned int count_remaining(unsigned int b, unsigned int b_max,
>> +                                           unsigned int *div_blocks)
> 
> this doesnt need to be inline, i belive its not speed critical, but rather
> handling just damaged bitstreams or am i misunderstanding the code?
Yes.

> 
> also maybe this one could do the memset as well
I had done this, but factored it out again because it would count the
remaining samples twice in case of joint-stereo.


>> +/** Decodes an ALS frame.
>> + */
>> +static int decode_frame(AVCodecContext *avctx,
>> +                        void *data, int *data_size,
>> +                        AVPacket *avpkt)
>> +{
>> +    ALSDecContext *ctx       = avctx->priv_data;
>> +    ALSSpecificConfig *sconf = &ctx->sconf;
>> +    const uint8_t *buffer    = avpkt->data;
>> +    int buffer_size          = avpkt->size;
>> +    int invalid_frame        = 0;
>> +    unsigned int c, sample, ra_frame, bytes_read, shift;
>> +
>> +    init_get_bits(&ctx->gb, buffer, buffer_size * 8);
>> +    ra_frame = sconf->ra_distance && !(ctx->frame_id % sconf->ra_distance);
>> +
>> +    // the last frame to decode might have a different length
>> +    if (ctx->num_frames && ctx->num_frames - 1 == ctx->frame_id) {
>> +        ctx->cur_frame_length = ctx->last_frame_length;
>> +    }
>> +
>> +    // decode the frame data
>> +    if ((invalid_frame = read_frame_data(ctx, ra_frame)))
>> +        av_log(ctx->avctx, AV_LOG_WARNING,
>> +               "Reading frame data failed. Skipping RA unit.\n");
>> +
> 
>> +    // increment the frame counter
>> +    ctx->frame_id++;
> 
> that wont work with seeking
> I think ive not missed some setting of frame_id to a value from the
> bitstream
No, it's selfmade. The decoder has to know, which frame it is in.
How to determine it in a seeking compatible way?


> 
> 
>> +
>> +    // transform decoded frame into output format
>> +    #define INTERLEAVE_OUTPUT(bps)                                 \
>> +    {                                                              \
>> +        int##bps##_t *dest = (int##bps##_t*) data;                 \
>> +        shift = bps - ctx->avctx->bits_per_raw_sample;             \
>> +        for (sample = 0; sample < ctx->cur_frame_length; sample++) \
>> +            for (c = 0; c < avctx->channels; c++)                  \
>> +                *dest++ = ctx->raw_samples[c][sample] << shift;    \
>> +    }
>> +
>> +    if (ctx->avctx->bits_per_raw_sample <= 16) {
>> +        INTERLEAVE_OUTPUT(16)
>> +    } else {
>> +        INTERLEAVE_OUTPUT(32)
>> +    }
>> +
>> +    *data_size = ctx->cur_frame_length * avctx->channels
>> +                 * (av_get_bits_per_sample_format(avctx->sample_fmt) >> 3);
> 
> i think you dont check data_size for being large enough
Added a check for data_size > INT_MAX in decode_init(). I hope this is
what you meant...


Everything else will be part of revision 11.

Thanks!

-Thilo